Once upon a Tom in Hollywood’s review published on Letterboxd:
Just think, one day your wife is cleaning the cat litter and she gets a worm in her, and that worm ends up in her brain. The next thing that happens is she gets an idea in there, too. And it's hard to say whether that idea is really hers or it's just the worm. And it makes her do certain things. Predator things. Eventually, you realize that she isn't the same person anymore. She's not the person that she used to be. It's gotta make you wonder, whether you're really married to her... or married to the worm.
Possessor is disturbing on so many levels. Yes, it's violent, gory, and unflinchingly brutal. But the moments that made me cringe the hardest were the ones that happened fully inside the mind. Psychological terror doesn't even begin to cover what this film puts you through.
A little more exposition and fleshing out of the characters would have made this a stronger film overall, but it's worth the price of admission as-is. Recommended, but definitely not for the faint of heart. Streaming now on Hulu.